Remain vigilant for TuYV
Growers have been warned to remain vigilant for turnip yellows
virus (TuYV) in the coming years, after latest findings showed that
70 per cent of peach potato aphids are carrying the virus.
British Beet Research Organisation
(BBRO) head of science, Dr Mark
Stevens, says that research has found
that the virus, which can affect oilseed
rape and other cover crops, had the
potential to cause blanket primary
infection if not dealt with effectively.
“For nearly 30 years, we’ve
been monitoring migrating aphid
populations for the sugar beet
virus yellows complex and TuYV,”

Dr Stevens explains. “Using 30 sites
around the UK, we caught almost
5,000 peach potato aphids during
the spring and summer of 2017 and
used a series of diagnostic tools
to test for viruses including TuYV.
The results showed that 7 out of 10
aphids are carrying the virus – this
is at the top end of the levels we’ve
found historically.
“If you’ve got such a high number
of infected aphids landing and
feeding on oilseed rape, you can
find that the whole crop can quickly
get infected. That means that it’s
essential that growers keep track of
migration, particularly as there is no
treatment threshold in oilseed rape.”

Timing

BBRO head of science, Dr Mark Stevens.

When it comes to controlling aphids
in oilseed rape, choosing the right
insecticide and ensuring timely
application are both key. Agrovista

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Results showed that 7 out of 10 aphids are carrying the TuYV virus.

technical manager Mark Hemmant
notes that though the risk period
for aphids has now passed, growers
still need to look out for the pests
moving forward.
“Early infestations tend to have
a bigger impact on yield, and in
high pressure years this can result
in losses of 25–30 per cent. Through
September and October 2017 we
urged agronomists and growers to
be vigilant in detecting aphids and
spraying them as soon as they see
them. On the other hand, if they
were found later, it would have been
a marginal call when it comes to the
cost of the spray against the cost of
the yield loss without a spray.”
He continues: “There’s a lot of

insecticide resistance in peachpotato aphids. You need to go for
a product like Biscaya (thiacloprid),
which is the fastest-acting and more
efficacious. TuYV is different to many
other viruses simply because such
a high proportion of aphids are
carrying it, so timing that insecticide
spray and getting it on as soon as
you spot any aphids is crucial.”
However, spotting aphids and
TuYV is not always straightforward.
Mr Hemmant points out that since
growers can’t be in the crop checking
every day, they should keep an eye

on aphid bulletins, such as Aphid
News by AHDB and Rothamsted
Research, for flights in their area.
“If there’s any sign in the autumn,
bring a hand lens out with you and
look carefully, because they’re not
always easy to see. You need to catch
the early ones – if you wait for them
to reproduce, it’s probably already
too late.
“Another key thing to remember
is that TuYV can be difficult to
diagnose: the symptoms – such as
reddening or purpling around the
margins of the leaves – are also seen
in crops when they’re under stress, or
when they have some trace element
deficiencies. Those factors can end
up being blamed for the loss of yield,
while the TuYV goes untreated. So it
can be a hidden yield robber.”
Dr Stevens agrees that
misdiagnosis can be a problem,
especially since there is a time lag
between the initial infection and
the symptoms appearing in the
crop. “You may get infection in the
autumn, but it might not show in
the crop until the following March
or April. So if you find TuYV in your
oilseed rape in the spring, you
need to watch for further migration
this year and be vigilant for virus
infection in future crops.”
Dr Stevens notes that although
much depends on winter weather,
high levels of TuYV mean growers
need to be on alert: “Cold weather
will kill a lot of the aphids in oilseed
rape. But if you have a high level
of infection, and you then get
fresh aphids coming in, there’s
every likelihood they’re going to
pick up the virus. The problem
isn’t necessarily an easy one for
growers to solve, but staying vigilant
and employing the right control
strategies are an important start.” ■